Hydrophobic coating compositions, articles coated with said compositions, and processes for manufacturing same

ABSTRACT

Hydrophobic coating compositions are provided as are processes to coat articles with the compositions. Extremely hydrophobic coatings are provided by the compositions. Durable, weatherable and scratch-resistant coatings are provided by compositions comprising a trifluoromethyl-containing component and a hardenable material. Processes are also provided for forming hydrophobic coatings on articles without any substantial loss of fluorocarbon solvent used in the coating composition. Articles are coated on a surface thereof with a hydrophobic coating reactant or reaction product which forms a coating having an exposed surface populated with 30% by area or more terminal trifluoromethyl groups.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation in part of U.S. patentapplication Ser. No. 08/795,316, filed Feb. 3, 1997, now U.S. Pat. No.5,853,894, issued Dec. 29, 1998.

FIELD OF THE INVENTION

The present invention relates to compositions for coating surfaces,surfaces coated with compositions, and methods of forming coatedsurfaces. More particularly, the present invention relates tohydrophobic coatings for laboratory vessels and other articles. Thepresent invention also relates to processes for forming a hydrophobiccoating on a surface of an article.

BACKGROUND OF THE INVENTION

Hydrophobic coatings are useful for many applications, for example, toprevent rain from wetting-out or collecting on a windshield. Anotherapplication of hydrophobic coatings is in the field of laboratoryvessels. Laboratory vessels including chambers, microtiter plates,vials, flasks, test tubes, syringes, microcentrifuge tubes, pipettetips, selectively coated microscope slides, coverslips, films, poroussubstrates and assemblies comprising such devices are often used tohandle, measure, react, incubate, contain, store, restrain, isolateand/or transport very precise and sometimes minute volumes of liquid,often biological samples. When samples are quantitatively analyzed, itcan be of critical importance that precise and representative amounts ofsample are transferred, or else inaccurate results are obtained. Due tothe different affinities of some materials to adhere to the walls of alaboratory vessel, qualitative analyses such as concentrations ofmaterials may also be adversely affected if certain materials in asample selectively adhere to operational surfaces of the vessel walls.

Unfortunately, materials typically used in the manufacture of laboratoryvessels do not sufficiently repel many biological sample fluids nor dothey sufficiently resist the adherence of molecular constituents of sucha sample fluid. The sample fluids often wet the surface of the vesselcausing residual quantities of liquid sample to cling to an operationalsurface of the vessel when the sample is removed. In some cases,significant quantitative and/or qualitative errors result. It istherefore desirable to provide extremely hydrophobic coatings forlaboratory vessels which will reduce the wetting of the operationalsurfaces of the vessels and reduce clinging by even the most adherentsamples so that virtually no sample remains in the vessel when poured,ejected or vacuumed therefrom.

In some laboratory techniques, it is important to restrain, isolate orlimit the position of liquid samples to prescribed locations within oron a laboratory vessel, while keeping adjacent surfaces of the vesselsubstantially free of liquid sample. Such techniques can be used tofacilitate chemical and biological reactions, as well as improvingsample recovery. The prescribed locations may (1) have surfaces that arereactive, (2) have a surface that exhibits a specific affinity, (3)optimize the sample volume to area ratio, (4) restrict sample movementduring at least some vessel motion, and (5) have porous surfaces.

Vessels for handling, measuring, storing and transporting liquids havepreviously been rendered less wettable and less adherent to fluids byapplication of silicone compounds to the vessel surfaces which come incontact with the fluid. For example, silane monomers and polymers havebeen added to polyolefins prior to injection molding, resulting inlaboratory vessels with an improved repellency to many sample fluids andtheir constituents. These materials produce surfaces with surfaceenergies potentially as low as 22 ergs per square centimeter. Inpractice, however, silane treated vessels exhibit surface energies thatmeasure 25 to 30 dynes/cm.

Drawbacks associated with silane treatments include a continued wettingof the vessel, adherence to the vessel walls by many samples, chemicalreactivity with many reagents, and a tendency for the vessel to becomewettable following the common practice of autoclaving for sterilization.Silicones are known to freely migrate, leading to worries over sampleintegrity. Many pipette tips are plugged with porous filters to preventsample contamination from the pipettor barrel, yet these free siliconesmake the pipette tips slippery and cause the filters to become loose ordislodged. Additionally, silicones must typically be added at a level of2 percent by weight to be effective, making the cost prohibitive formany price sensitive applications.

Fluorination processes have been used to treat laboratory vessels andhave resulted in vessels having interior surfaces with surface energiesapproaching 22 dynes/cm. These processes generally involve the full orpartial replacement of superficial hydrogen by fluorine using chemicalprocesses or the plasma polymerization of fluorine containing gases.U.S. Pat. No. 4,902,529 to Rebhan et al. discloses a plasma torchprocess using CF₄ or SiF₆ to fluorinate the interior of resin articlesand containers in an attempt to eliminate the use of dangerous mixturesof fluorine and inert gases. This method is impractical, however, fortreating the vast quantities of small vessels consumed by industrial,clinical and research establishments. Furthermore, improvements inperformance over silicone processes are only marginal.

The plasma polymerization of perfluorobutene onto the exterior surfaceof various articles has been reported to produce exterior surfaces withup to 24 percent --CF₃ groups, and a high percentage of --CF₂ -- groups.Resultant surface energies of 22 to 24 dynes/cm are obtained due to thepresence of cross-linkages and numerous monofluorinated carbons.Time-consuming, carefully controlled RF plasmas employingfluorine-containing monomers have also been used to reduce thewettability and adhesion of laboratory vessels, producing exteriorsurface energies of 12 to 15 dynes/cm and surface populations of up toabout 25% by area CF₃ groups on exterior non-operational surfaces.Interior operational surfaces, however, are still not reduced to below22 dynes/cm. While these methods offer improvements over silicon-basedtreatments, the time, expense and equipment required are not appropriatefor high commercial volume articles that are often for one-time use andrequire very low inherent cost.

Perfluoroalkyl polymers and carefully prepared monolayer films ofperfluoroalkyl surfactants are widely recognized as having surfaceenergies below 20 dynes/cm. FEP and PFA Teflons®, available fromDuPont's Polymer Products Department, Wilmington, Del., have surfaceenergies of 15 to 16 dynes/cm with --CF₃ populations as high as 25percent. Extruded and fused Teflon® vessels are currently manufacturedfor special applications involving exceptionally harsh reagents but areexpected to have a long service life because of their high material costwhen compared to the cost of glass or polypropylene vessels.

Fluoroalkyl polymers have been used to produce oleophobic, hydrophobicmembrane surfaces that are not wetted by common organic solvents.Membranes coated with such polymers are disclosed in U.S. Pat. No.4,954,256 to Degen et al. These membranes have surface energies rangingfrom about 6 to about 15 dynes/cm but require a manufacturing procedurewhich involves soaking a membrane with a solution containingpolymerizable monomers, exposing the solution-wetted membrane to highdoses of ionizing radiation, and then washing the ionized membrane withorganic solvent to remove unreacted monomer. While no attempts are knownto coat laboratory vessels by such a procedure, it is expected thatdifficulties would arise as well as high cost in coating such vesselsbecause of the shear bulk of the polymerizable solution to be irradiatedand problems with fully washing the coated vessel.

Methods of making disposable, one-time use laboratory vessels such aspipette tips can involve a substantial loss of costly solvent when acoating solution is used to form a hydrophobic coating. A need existsfor a process of coating laboratory vessels at a cost of a few cents perthousand with an insignificant loss of solvent.

Recent patents may suggest the practice of solvent recovery in theapplication of certain branched fluoropolymers, such as Teflon AF, toarticles of manufacture. U.S. Pat. Nos. 5,356,668 to Paton et al. and5,006,382 to Squire are incorporated herein in their entireties byreference. The mere suggestion of such a recovery practice, however,does not provide a commercially viable method for coating many low cost,one-time-use articles, such as pipette tips and laboratory vessels.

Environmental concerns about pollution by volatile solvents, especiallychlorine-containing materials such as perchoroethylene, have motivatedsignificant improvement in dry cleaning equipment, resulting insignificant reductions in solvent losses. Cleaning and coating equipmentused in the semiconductor, plastics, and metal parts industries havemade similar strides. Better seals and welded ducts account for some ofthe upgrades.

Operation of these machines according to their suggested protocols usingfluorinated solvents, however, still results in large, expensive losses.For example, the Renzacci Company of Italy manufacturesperchloroethylene-based cleaning machines that are widely recognized tobe among the best in the industry in terms of minimal solvent loss. Butloaded with 60,000 pipette tips in mono-filament mesh bags and usingRenzacci's standard automated programs, these machines lose about 5pounds of FC84 (3M Company, St Paul, Minn.) per cycle. This translatesto solvent consumption costs of over one dollar per thousand tips.Higher boiling point fluorocarbon solvents have lower loss rates, butthe solvent expense is about the same due to their higher cost perpound.

The Renzacci standard automated program partially fills acleaning/coating tank of approximately one-half cubic meter with solventat ambient temperature from a solvent reservoir. Articles in the tankare then tumbled in the solvent for several minutes, followed by drain,spin and spin-rinse cycles. With continued tumbling, a heat pump and asupplementary heat source (electric, steam, etc.) heat air blown throughthe tank, while passing air returns from the tank over chilledcondensation coils where solvent vapor is liquified and returned to thereservoir. Water is circulated through the heat pump system to removeexcess heat. However, the temperature in the tank can still rise to over50° C. and the reservoir temperature can rise to more than 30° C. At theend of the process cycle, heating is discontinued and the tank andreservoir are cooled to about 30° C. When the tank door is opened toremove the cleaned/coated articles, a small blower draws air out of thetank through a carbon filter in order to reduce the odor of remainingperchloroethylene solvent.

Unfortunately, at 30° C. the solvent FC84 has a vapor pressure of overone fifth atmosphere, and the half cubic meter tank volume containsabout two pounds of solvent as dense vapor (about 14 times that of air),even without agitation. Opening the tank door results in the immediateloss of this material, at a current cost of about $45 (US). Since themachine will handle about 60,000 tips per run, the loss per thousand isabout 50 cents. The carbon recovery filter is at the top of the tank andis of little practical economic value.

Additional losses accrue during the heat cycle at 50° C. when themachine fittings and seals are challenged by pressures approaching 1.2atmospheres. Furthermore, it is apparent from other studies that lowmolecular weight fluorocarbon solvents, having boiling points between80° and 120° C. are particularly "slippery" in passing through rubberand silicone gaskets and seals. No machines investigated had moreaggressive containment systems for leak-free operation under theseconditions.

A need exists for a method of coating large numbers of laboratoryvessels which results in a very low loss of solvent at a surprising andsignificant cost savings.

Described by Dettre and Johnson in 1964 are phenomena related to roughhydrophobic surfaces. Dettre and Johnson developed a theoretical modelbased on experiments with glass beads coated with paraffin or TFEtelomer. For even moderately hydrophobic surfaces (e.g. about 40dynes/cm or less) with high levels of microscopic roughness, where theaverage height of bumps is close to or exceeds their average width, anaqueous liquid, especially one without surfactant activity, in contactwith the surface only wets the top of the bumps, forming what is knownas a "composite" air-liquid-solid interface. For example, water at reston a surface of this kind may exhibit contact angles greater than 160degrees. This unusual property has been practiced and is the basis for avariety of proprietary microscope slide, plate and membrane productsusing coatings sold by Cytonix Corporation, in Beltsville, Md. However,such products are based on Teflon® and the hydrophobic properties ofdifluoromethylene (--CF₂ --) groups, which at best exhibit surfaceenergies of from about 18 to about 20 dynes/cm.

A need exists for a method of manufacturing a coating which exhibits, onall or part of an operational surface thereof, interfacial contactangles to aqueous samples of 120° and above, even as high as 160°, andsurface energies well below 20 dynes/cm. According to some desirableapplications, a need also exists for vessels having surface energies ofbelow 10 dynes/cm. This need is especially acute but difficult toachieve for one-time-use vessels costing only a few dollars perthousand.

There is also a need for extremely hydrophobic coatings that aredurable, for example, coatings for articles such as windshields,rainshields, and satellite and/or radar dishes, other signal receiversand transmitters, and radomes. A need exists for a composition which canprovide an extremely hydrophobic and durable coating on a surface of anarticle. Problems associated with water film formation on radomes, andproblems of radar desensitization in rain are described, for example, inthe Honeywell Technical Newsletter entitled RADAR DENSENSITIZATION INRAIN, WATER FILMS ON RADOMES, AND HYDROPHOBIC COATINGS, Nov. 2, 1998,republished by Cytonix Corporation with permission from Honeywell, Inc.,said newsletter being incorporated herein in its entirety by reference.A need exists for a coating composition for a signal transmitter orreceiver, wherein the composition can be applied and form an extremelyhydrophobic coating that does not interfere with signal transmission orreception.

A need also exists for a composition which forms a hydrophobic surfaceuseful as a surface for articles which could benefit from hydrophobicproperties, for example, vehicular surfaces, architectural surfaces,outdoor furniture, household goods, and kitchen and bath articles.

SUMMARY OF THE INVENTION

According to the present invention, extremely hydrophobic coatings areprovided. According to an embodiment of the present invention, theinvention provides a durable, weatherable, and erosion-resistanthydrophobic coating. The coatings of the present invention can be usedon a signal transmitter or receiver, for example, a microwave,infra-red, light, radar, electromagnetic, or the like emitter orreceiver such as a radome. The coatings of the invention do notadversely affect reception or transmission of a signal.

According to another embodiment of the present invention, a process isprovided for forming an extremely hydrophobic coating on a surface of anarticle. An embodiment of the present invention is based on thediscovery that methods can be provided to coat laboratory vessels withan extremely hydrophobic coating at a cost of only a few cents perthousand vessels.

According to embodiments of the present invention, a surface is coatedwith a composition which includes or provides a reaction product, forexample, a polymerization product, of a fluorinated reactant, forexample, a fluorinated monomer containing from about 3 to about 20carbon atoms and at least one terminal trifluoromethyl group. Accordingto embodiments of the invention, the coating composition also includes ahardenable material, for example, a urethane resin or TEFLON AF fromDuPont. Hardenable materials that may be employed includenon-fluorinated hardenable resins, fluorinated hardenable resins, andperfluorinated hardenable resins. The resulting surfaces are extremelyhydrophobic and highly resistant to removal by weathering and/orsolvents.

Herein, the term "fluorinated" includes both perfluorinated andnon-perfluorinated monomers and/or polymers. The present inventionrelates to fluorinated compositions, coatings, and coated surfaces whichmay be part of or parts of laboratory vessels, signal transmitters,signal receivers, signal reflectors, radomes, vehicular surfaces,architectural surfaces, outdoor furniture, household goods, kitchenarticles, kitchen surfaces, bathroom articles, bathroom surfaces,antennae, microwave antennae, dishes, reflectors, signs, visualsignaling devices, scanner windows, lenses, liquid crystal displays, andvideo displays. In addition, the present invention relates to processesof coating small article surfaces, for example, laboratory vessels, withnominal solvent loss.

Processes of forming the extremely hydrophobic coatings of the presentinvention may include applying a solution, suspension or other liquidcontaining a coating composition and allowing the solution, suspensionor other liquid to harden, dry and/or cure on a surface. The coatingcomposition includes a trifluoromethylated agent, which may be areactant, a monomer, a reaction product, and/or a polymerizationproduct. The present invention also provides a method wherein a solutionor suspension of such agent is partially, selectively or conformallycoated onto at least a portion of a surface of an article, for example,a laboratory vessel, a radar dish, a radome, a windshield, a rainshield,a vehicular surface, an architectural surface, outdoor furniture, ahousehold good, a kitchen article, a kitchen surface, a bath article, abathroom surface, an antenna, a microwave antenna, a dish, a reflector,a sign, a visual signaling device, a scanner window, a lens, a liquidcrystal display, and/or a video display. Then, the composition includingthe agent is subsequently hardened, dried, and/or cured to removesolvent and/or suspension medium. The coatings provide surfacesexhibiting extremely low surface energies and, for some cases,preferably also provide a high resistance to solvent removal. Somecompositions according to the present invention may desirably be removedwith one or more organic solvent, for example, with methylethylketone(MEK).

A surprising discovery about the economics and commercial success ofcoating low cost, especially one-time-use, articles with fluoropolymercoatings is that process efficiency in recovering carrier solvents canbe a more important factor than the relatively high cost of the coatingfluoropolymers. While high quality unsaturated fluoromonomers currentlycan cost $250 (US) to over $1000 (US) per pound in bulk quantities,articles such as pipette tips may only require 10 to 20 milligrams offluoropolymer per thousand pipette tips at a current cost of less than10 cents per thousand. Conventional coating/washing equipment, forexample, equipment from Renzacci of America Inc., Absecond, N.J., andfrom Fluoromatic Ltd., Villa Park, Ill., and processes that are designedto recover solvents, can consume over 25 grams of solvent per thousandpipette tips at a current cost of about five cents per gram or $1.25(US) per thousand. In many situations, particularly coating methodsusing expensive perfluoropolymers, this is an unacceptable added cost toarticles otherwise costing only a few dollars per thousand tomanufacture. According to the present invention, solvent loss issignificantly reduced compared to the conventional machines andprocesses.

According to some embodiments of the invention, a hydrophobic coatingmay be formed from a coating composition of the invention applied orco-injected as a resin, powder, particle or mixture which is dried,melted, sintered, fused cured or otherwise formed on a surface of anarticle.

Moreover, the present invention is based on the discovery thatlaboratory vessel surfaces of low surface energy can be provided bycoating a solution, suspension, other liquid, resin, powder, particle ormixture of a trifluoromethylated agent according to the invention,admixed with microscopic particles and/or fibers. In some embodiments,foaming and/or pore-forming agents may additionally, or alternatively,be admixed with the coating compositions of the present invention. Thetrifluoromethylated agent may include a trifluoromethylated reactant,monomer, reaction product and/or polymerization product. Upon subsequentdrying, melting, solidifying, sintering, fusing or curing of the coatingformulation, a laboratory vessel is produced exhibiting extraordinarilyhigh contact angles to aqueous liquids.

The present invention is also based on the discovery that coatings oftrifluoromethylated agents containing 3 to 20 carbon atoms and at leastone terminal trifluoromethyl group are extremely hydrophobic and canprovide populations of 30% by area or greater of trifluoromethyl groupson exposed coating surfaces. According to the present invention, areaction product of a reactant trifluoromethylated agent may be coatedfrom a formulation onto at least a portion of an operational surface ofa laboratory vessel, for example, a vessel surface which contacts orrestrains a liquid sample. The coatings have tightly packed, exposedtrifluoromethyl groups.

According to some embodiments, at least about 30% of the area of theexposed coating surface is covered by trifluoromethyl groups. Accordingto more preferred methods of the invention, the exposed coating surfaceis covered with a population of trifluoromethyl groups of from about 50%to 100% by area of the surface. According to some embodiments, at leastabout 15% by area of the exposed coating surface is covered bytrifluoromethyl groups and the coating includes a hardenable resin inaddition to a reaction product of a trifluoromethylated agent.

According to the present invention, the coating composition comprises atrifluoromethylated agent comprised of a fluorocarbon,hydrofluorocarbon, epoxy, urethane, silicone, acrylic or other materialthat has a terminal trifluoromethyl group and contains from about 3 toabout 20 carbon atoms. Preferably, coatings made from such compositionsexhibit tightly packed trifluoromethyl groups on the exposed coatingsurface. According to some embodiments of the invention, coatingpolymers made from substantially non-branched fluorinated monomershaving carbon chains of from about 3 to about 20 carbon atoms in length,and more particularly from about 6 to about 12 carbon atoms in length,enable a dense packing of the terminal trifluoromethyl groups and thuscan form hydrophobic surfaces of very low surface energy, havingcritical surface tensions of about 10 dynes/cm or lower at 20° C., andhaving high resistance to solvent removal and low retention ofbiological samples.

According to yet other embodiments of the invention, laboratory vesselsand other articles are coated with hydrophobic coating formulationscontaining terminal trifluoromethyl groups and optionally furthercontaining reaction products, polymers, reactants, polymerizablemonomers and/or other additives which also become incorporated in thehydrophobic coatings.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, an extremelyhydrophobic coating can be formed on the surface of an article andcomprises the reaction product of a reactant containing a terminaltrifluoromethyl group. According to embodiments of the presentinvention, an extremely hydrophobic coating can be formed from acomposition consisting essentially of the reaction product of a reactantcontaining a terminal trifluoromethyl group with or without a hardenableresin, for example, a urethane resin. Particular articles which can becoated according to the present invention include those having anoperational surface comprising plastic, sintered material, wovenmaterial, textured material, semiconductor, glass, ceramic, or metal, ora primed or pre-coated surface. The invention can also be used onoperational surfaces which are porous, smooth, rough, pitted, foamed,grooved, cross-hatched, striated, or having patterned physical features.

Laboratory vessels according to an embodiment of the present inventionhave at least one operational surface. Many vessels according to theinvention have at least one interior wall which defines a reservoirportion for containing a volume of liquid, and at least one opening incommunication with the reservoir portion. According to some embodimentsof the invention, a laboratory vessel having an interior wall and anopening is coated on the interior wall and on the area surrounding andforming the opening, with a polymer coating according to the invention.

According to embodiments of the present invention, methods are providedfor forming extremely hydrophobic coatings on small articles such aslaboratory vessels. Measures to curtail fluorinated solvent losses,according to the present invention, focus on better containment,improved solvent recovery, and reduced solvent vapor pressure throughoutthe coating operation. According to embodiments of the invention, thegeneral design of the Renzacci Patriot 350, from Renzacci of America,may be employed for the coating machine and process of the presentinvention, but with some major modifications. According to the presentinvention, it has been determined that rubber and silicone seals aresignificantly not leak-proof to fluorocarbon solvents. According to thepresent invention, sealing means comprising a rubber derived fromvinylidene fluoride and hexafluoropropene, for example, VITON™ seals aresubstituted for other rubber or silicone seals. The generally lowerpermeability of VITON™ seals to hydrophobic gases such as methane andtetrafluoromethane prevent a significant amount of fluorocarbon solventand/or gas loss as a result of a coating process.

Metal tubing and swaged fittings are preferred over plastic piping andthreaded pipe connections. If the Renzacci machine is modified to forman apparatus according to the present invention, the carbon "recovery"system of the Renzacci model is preferably eliminated.

According to embodiments of the present invention, solvent recovery isenhanced by lowering the cooling coil temperature and by slowing the airflow over the coils. Longer recovery times are programmed to furtherimprove solvent recovery according to embodiments of the presentinvention. According to embodiments of the invention, significantbenefits in reducing solvent loss are achieved by operating the entirecoating cycle at temperatures that keep solvent vapor pressure lowrelative to atmospheric pressure, that is; at about or below atmosphericpressure. Although removing solvent from wetted articles according tothe invention requires somewhat more time, the increased cost of machinetime is only hundredths of a cent per thousand pipette tips. Solventconsumption, however, is reduced to only barely detectable levels,providing overall savings of more than $60 (US) per cycle.

According to embodiments of the present invention, a process is providedwherein laboratory vessels can be coated with a composition which formsa coating having at least a 15% by area trifluoromethyl surface, andsolvent loss resulting from the process of less than 20 grams offluorosolvent lost per pound of processed laboratory vessels. Morepreferably, solvent loss resulting from the process is less than 10grams of fluorosolvent lost, more preferably less than 5 grams offluorosolvent lost, per pound of processed laboratory vessels. Even morepreferably, fluorosolvent loss according to an embodiment of the presentinvention is only one gram of fluorosolvent lost per one pound ofprocessed laboratory vessels.

According to embodiments of the present invention, a process is providedwherein articles, for example, laboratory vessels, can be coated with acomposition which forms a coating having at least a 15% by areatrifluoromethyl surface, and solvent vapor pressure within the coatingchamber is maintained substantially below atmospheric pressure.Preferably, solvent vapor pressure within the coating chamber ismaintained at below about 25% of atmospheric pressure, more preferably,at below about 10% of atmospheric pressure, for example, below about 5%of atmospheric pressure. Even more preferably, solvent vapor pressure ismaintained at less than 1% of atmospheric pressure. Temperature controlcan be used to maintain low pressure. The solvent loss is substantiallyminimized according to the process of the present invention whereinafter coating the articles the seal of the sealed chamber is brokenwhile the vapor pressure within the chamber is below atmosphericpressure, preferably below about 25% of atmospheric pressure.

According to the present invention, laboratory vessels are provided withcoatings having at least a 15% surface area population oftrifluoromethyl groups by a process wherein solvent temperature ismaintained substantially below its boiling point during the coating andsolvent recovery process. Preferably, a fluorinated solvent is used.Preferably, solvent temperature is maintained below 75%, for example,below 50% of the absolute value of the difference between the boilingpoint of the solvent and 25° C. For example, if the solvent has aboiling point of 85° C., the temperature is preferably maintained at orbelow 70° C., which is at or below 75% of the absolute differencebetween 85° C. and 25° C. More preferably, solvent temperature ismaintained below 25% of the absolute value of the difference between theboiling point of the solvent and 25° C. Cooling water chillers or heatexchangers can be used, for example, to lower the temperature of thecoating solution or suspension.

Articles such as laboratory vessels to be coated according to a processof the present invention may contain or consist of plastic, metal, orglass. Preferred materials used to manufacture the coated laboratoryvessels of the present invention include polypropylene, polyethylene,polyethyleneterephthalate, polystyrene, polycarbonate and cellulosics.More expensive plastics such as polytetra-fluoroethylene and otherfluorinated polymers may be used. Some vessels made from these plasticsare hydrophobic without any additional coating. Herein, the term"hydrophobic" refers to a surface exhibiting an average surface energyof about 40 dynes/cm or less. Because polypropylene is inexpensive andquite hydrophobic itself, it is a particularly preferred material forlaboratory vessels, including pipette tips, used for handling andtransporting minute and precise amounts of biological sample.

In addition to the materials mentioned above, examples of other suitablematerials for the laboratory vessels of the present invention includepolyolefins, polyamides, polyesters, silicones, polyurethanes, epoxies,acrylics, polyacrylates, polyesters, polysulfones, polymethacrylates,polycarbonate, PEEK, polyimide, polystyrene, and fluoropolymers such asPTFE Teflon®, FEP Teflon®, Tefzel®, poly(vinylidene fluoride), PVDF, andperfluoroalkoxy resins. Glass products including silica glass are alsoused to manufacture laboratory vessels. One exemplary glass product isPYREX® (available from Corning Glass, Corning, N.Y.). Ceramic or oxidesurfaces can be coated according to embodiments of the invention.Cellulosic products such as paper and reinforced paper containers can becoated to form coated laboratory vessels according to the invention.Metal surfaces can be coated according to the invention, as can surfacesof glass, silicon, silicon compounds or ceramics that have or have notbeen primed with silane containing materials or other adhesion promotingmaterials. Primed metal, primed glass, primed ceramic and primed oxidesurfaces can be coated according to embodiments of the invention. Vesselsurfaces that have been pre-coated with epoxies, silicones, urethanes,acrylics, or other materials can also be coated according to embodimentsof the invention.

Although some wash-off of polymerized coating material or coatingmonomer might be expected after repeated usage, the coatings of thepresent invention do not measurably wash off most laboratory vesselsurfaces. It is believed that little if any wash-off occurs because thecoating solution causes softening and swelling of the vessel material,especially in uncross-linked plastics, and enables entanglement ofcoating and vessel substrate molecules allowing strong Van der Waals andother bonding forces which hold the prepolymerized product where appliedto an operational surface of the vessel. The linear swelling of manypolymers and elastomers, including some fluoroelastomers and somesilicones, is reported in Table 8 of the 1996 Technical Informationsheet for Vertrel™ XF, available from DuPont's Polymer ProductsDivision, Wilmington, Del. Little if any wash-off occurs from othervessel materials because of the extremely low solubility of the coatingsof the present invention in most solvents and limited solubility influorinated solvents. Preferably, even exposure to water wash conditionsof 1500 psi causes no substantial reduction in hydrophobic properties ofthe coating or material having a surface of the present invention.

According to some embodiments of the present invention, hydrophobicreaction products having terminal trifluoromethyl groups are coated froma fluorinated agent/fluorosolvent solution or suspension onto linear,hydrophobic, essentially uncrosslinked polymers such as polyolefins andTEFLON®, and show particular resistance to removal even by chlorinatedsolvents. According to the present invention, swelling of the polyolefinsurface during application of the fluorinated agent solution orsuspension and subsequent entanglement of the reaction product, forexample, polymerization product, at the interface, result in stronghydrophobic bonds between the coating and the polyolefin surface.Surprisingly, the coatings according to embodiments of the invention arenot measurably removed, even with chloroform or chloroethene.

According to some embodiments of the invention, the laboratory vesselcomprises a microscope slide or other substantially flat device havingan operational surface at least partially coated with a coatingformulation according to the invention. According to some embodiments ofthe invention, a delineated area of a laboratory vessel surface, forexample, a portion of the surface of a microscope slide, is not coatedwith the coating formulation, but is instead surrounded by the coating.The coating thus forms a boundary to restrain, contain or isolate afluid sample on the non-coated area of the surface, while adjacentsurfaces remain free of liquid sample, thus isolating and facilitatingchemical and biological reactions as well as improving sample recovery.The uncoated locations may have surfaces that, for example, are reactiveor have specific affinities, optimize the sample volume to area ratio,or restrict sample movement during some vessel motion. The uncoatedregion may be surrounded by a hydrophobic coating material according tothe invention which comprises microparticles and the reaction product,for example, the polymerization product, of a trifluoromethyl-containingreactant, for example, a trifluoromethyl-containing monomer.

According to some embodiments of the invention, the operational surfaceof a vessel such as a microscope slide is partially coated with ahydrophobic coating formulation according to the invention and partiallycoated with nonfluorinated material in delineated regions to isolate orconstrain the position of a liquid sample to prescribed locations thatdo not contain the hydrophobic coating formulation.

According to embodiments of the invention, an operational surfacecomprises a sample retaining barrier of a rough surface compositecoating according to the invention. The barrier may isolate and restrainan aqueous sample. Surrounding the composite coating may be a smoothcoating material which does not contain a sufficient amount ofmicroparticles and does not exhibit surface roughness. The surroundingsmooth coating permits the run-off of non-aqueous liquids therefrom,such as organic solvents, for example, acetone or xylene.

According to some embodiments, a laboratory vessel is provided with alow surface energy coating of the present invention and furthercomprises a second coating. The second coating comprises the reactionproduct, for example, the polymerization product, of a secondfluorinated reactant, for example, a fluorinated monomer. The secondfluorinated reactant preferably has from about 3 to about 20 carbonatoms, at least one terminal trifluoromethyl group, and is combined witha surface roughening agent, for example, a micropowder which providesthe second coating with a rough surface. The second coating has anexposed surface area populated with 30% by area or more trifluoromethylgroups and a surface energy of about 22 dynes/cm or less at 20° C. Thesecond coating forms a continuous sample retaining barrier for retainingan aqueous sample within the barrier, and the low surface energy coatingis substantially free of surface roughness and surrounds the secondcoating.

Articles other than laboratory vessels can also be coated with twodifferent coating compositions according to embodiments of the presentinvention. According to some embodiments of the present invention, anarticle is coated with a first composition and then with a second,different, composition. At least one of the coatings, for example, thefirst coating, preferably comprises the polymerization product of atleast one fluorinated monomer. At least one of the coatings can comprisethe polymerization product of tetrafluoroethylene. At least one of thecoatings can comprise the polymerization product ofperfluoro-2,2-dimethyl-1,3-dioxole (PDD). At least one of the coatingscan comprise the polymerization product of tetrafluoroethylene and PDD.Preferably, both coatings provide a trifluoromethyl group surface areapopulation of about 15% by area or greater, more preferably, of about30% by area or greater.

According to embodiments of the invention, regions on a surface of alaboratory vessel such as a microscope slide are used to isolate orconstrain aqueous sample, and the regions are defined by a first coatingcomprising microscopic particles and the reaction product of atrifluoromethyl-containing reactant. The first coating may surround aportion of a surface coated with a second coating wherein the secondcoating comprises the reaction product of a trifluoromethyl-containingreactant. The microparticle-containing coating provides a greaterhydrophobicity to aqueous liquids and thus a greater water repellingnature than the region coated with the polymerization product coatingthat does not contain the microparticles.

In some embodiments of the present invention, microscopic fibers such ascellulose or glass microfibers may be used with or in place ofmicroparticles to provide surface roughness and preferably contactangles to water of about 150° and greater. Preferably, cellulose and/orglass microfibers are used which have average diameters of from aboutone to about 20 microns and lengths from about 20 to several hundredmicrons. The microfibers can be admixed to increase the mechanicalstrength of the coating.

According to embodiments of the invention, rough hydrophobic surfaceshaving a high repellency to water may be produced by employing foamingand/or pore-forming agents in the compositions and processes of theinvention. Foaming and pore-forming agents that may be used includespirocarbonates, diazo compounds, compressed gases, dissolved gases,volatile liquids, and combinations thereof. The agents may be activatedby heat, light, or vacuum during the drying, curing and/or hardening ofthe coating composition.

According to embodiments of the invention, regions on a surface of alaboratory vessel such as a microscope slide are used to isolate orconstrain an organic solvent-based liquid sample, and the regions aredefined by a coating comprising the reaction product of atrifluoromethyl-containing reactant, surrounding a portion of thesurface coated with a formulation comprising microparticles and thereaction product of a trifluoromethyl-containing reactant. Themicroparticle-containing coating provides a greater affinity to organicsolvent-based liquids than the region coated with the reaction productcoating not containing the microparticles.

A preferred coating is provided by adhering a surface roughening agent,for example, a micropowder, to the surface of a reaction productaccording to the present invention, wherein the coating has an exposedsurface area populated with 30% or more trifluoromethyl groups. Apreferred coating can be formed with a surface roughening agent having asurface area populated with 30% by area or more trifluoromethyl groups,wherein the surface roughening agent is adhered to a hydrophobicsurface. The adherence of the surface roughening agent to the surfacemay be due to one or more mechanisms including, but not limited to,sintering the agent onto the surface, curing a component of the surfaceand/or a component of the agent, melting the surface and/or the agent,and the like, or any combination thereof. The surface roughening agent,for example, a micropowder, can be dusted onto the surface.

The present invention also provides processes of preparing surfaceroughening agent-containing hydrophobic surfaces. According to anembodiment of the invention, a hydrophobic coating formulation isapplied to a surface of an article to form a coating having an exposedsurface area populated with at least 30% by area trifluoromethyl groups.Then, fluidized hydrophobic surface roughening agent microparticles areapplied and adhered to the coating to provide a rough surface having anexposed surface area populated with at least 30% by area trifluoromethylgroups. The adherence of the agent to the coating may be due to one ormore mechanisms including, but not limited to, sintering the agent ontothe surface, curing a component of the coating and/or a component of theagent, melting the coating and/or the agent, and the like, or anycombination thereof.

According to an embodiment of the invention, a hydrophobic coatingformulation is applied to a surface of an article to form a coatinghaving an exposed surface area populated with at least 30% by areatrifluoromethyl groups. Then, fluidized hydrophobic surface rougheningagent microparticles having an exposed surface area populated with atleast 30% by area trifluoromethyl groups are adhered to the coating toprovide a surface having a population of trifluoromethyl groups of 30%by area or more. The adherence of the agent to the coating may be due toone or more mechanisms including, but not limited to, sintering theagent onto the surface, curing a component of the coating and/or acomponent of the agent, melting the coating and/or the agent, and thelike, or any combination thereof.

According to some preferred embodiments of the invention, laboratoryvessels are provided having an operational surface coated with a polymercomprising the polymerization product of trifluoromethyl-terminated,substantially unbranched and fluorinated monomers containing from 6 to12 carbon atoms. Coatings made from such products are extremelyhydrophobic, oleophobic, and highly resistant to solvent removal andbiological sample retention.

A particularly preferred coating solution for forming coatings accordingto the invention comprises the polymerization product of atrifluoromethyl terminated, substantially unbranched perfluorooctylmonomer. Coating solutions containing at least about 50% by weight of aproduct of such a perfluorooctyl monomer are particularly preferred forprinting applications.

The coating compositions of the present invention may be diluted with anappropriate solvent or medium to obtain a coating solids content of fromabout 0.01% by weight to about 50% by weight, preferably from about 0.1%by weight to about 2% by weight, depending upon the applicationtechnique and desired coating properties.

According to an embodiment of the present invention, a coatingcomposition is provided for forming an extremely hydrophobic coatingsurface on the surface of an article, wherein the composition includes afluorosilane, a fluorinated acid anhydride or fluoroanhydride, and afluorinated solvent. The fluorosilane may preferably be used in anamount of from about 0.1% by weight to about 50% by weight, for example,2% by weight, based on the weight of the composition. The fluorosilaneis preferably a fluoroalkylsilane. More preferably, the fluorosilane mayinclude a fluoroalkyl alkoxysilane, for example, perfluorooctyltrimethoxysilane. The fluorinated acid anhydride or fluoroanhydridepreferably is capable of a condensation reaction with an oxide surfaceto form an extremely hydrophobic surface, and preferably reacts underambient conditions or under heat. The fluorinated acid anhydride orfluoroanhydride may comprise, for example, trifluoroacetic acidanhydride, trifluorobutyric acid anhydride, and combinations thereof,both available from Aldrich Chemicals. The fluorinated solventpreferably has a boiling point above 100° C. Preferred fluorinatedsolvents include FC 70 (boiling point of 215° C.), and FC 40 (boilingpoint 155° C.), both available from 3M.

The terminal trifluoromethyl groups of the coating polymer or monomerpreferably constitutes the entire operational surface of the coating.According to preferred embodiments of the invention, the polymer coatingis applied in a manner such that the exposed coating surface comprisesfrom about 30% by area to about 100% by area trifluoromethyl (--CF₃)groups. In other words, of the molecules and substituent groups makingup the exposed operational surface of the coating, from about 30% byarea to 100% by area of the exposed surface area of the coating is madeup of --CF₃ groups. The exposed surface of the coating exhibits anextremely low surface energy which can approach about six dynes/cm,depending upon the percentage or "population" of --CF₃ groups making upthe exposed surface of the coating and the vessel material coatedaccording to the invention. In more preferred embodiments of theinvention, from about 50% by area to 100% by area of the exposed surfaceis populated with trifluoromethyl groups, and even more preferably, atleast about 75% by area is populated with trifluoromethyl groups.

The hydrophobicity and solvent resistance of the operational surfacecoating of the invention depends on a number of factors including thematerial of the laboratory vessel which is coated and the amount orpopulation of terminal trifluoromethyl groups present on the exposedsurface of the coating. For example, it has been determined according tothe invention that when an operational surface of a polypropylene vesselis coated with a hydrophobic polymer solution to form a coatingcomprising 30% by area or more trifluoromethyl-terminated, substantiallyunbranched perfluorinated monomer having from 6 to 12 carbon atoms, thecoating exhibits a surface energy of below 20 dynes/cm with highresistance to solvent removal and low retention of biological samples.

It has also been determined according to the invention that when anoperational surface of a polypropylene vessel is coated with ahydrophobic polymer solution to form a coating comprising 50% by area ormore trifluoromethyl-terminated, substantially unbranched perfluorinatedmonomer having from 6 to 12 carbon atoms, the coating exhibits a surfaceenergy of below 15 dynes/cm with high resistance to solvent removal andlow retention of biological samples.

It has also been determined according to the invention that when anoperational surface of a polypropylene vessel is coated with ahydrophobic polymer solution to form a coating comprising 80% by area ormore trifluoromethyl-terminated, substantially unbranched perfluorinatedmonomer having from 6 to 12 carbon atoms, the coating exhibits a surfaceenergy of about 10 dynes/cm with high resistance to solvent removal andlow retention of biological samples.

It has also been determined according to the invention that when anoperational surface of a polypropylene vessel is coated with ahydrophobic polymer solution to form a coating comprising 100% by areaor more trifluoromethyl-terminated, substantially unbranchedperfluorinated monomer having from 6 to 12 carbon atoms, the coatingexhibits a surface energy of below 10 dynes/cm or lower with highresistance to solvent removal and low retention of biological samples.

The most hydrophobic properties are achieved when the coating has anexposed surface consisting entirely of trifluoromethyl (--CF₃) groups,that is, 100% by area, with no other substituent groups exposed at thesurface.

According to some embodiments of the invention, branched fluoroalkylmonomers containing terminal trifluoromethyl groups may also be used asreactive monomers or polymerized product in the coating solutions usedaccording to the present invention. An example of a suitable branchedmonomer for such purposes is a perfluorinated iso-octyl monomer havingtwo terminal trifluoromethyl groups.

According to embodiments of the invention, the carbon chain length ofthe trifluoromethyl-containing monomers used to form the polymercoatings of the invention, and any functional groups used to formlinkages between the fluoropolymer and the laboratory vessel, should beselected to provide an exposed surface of the coating which mainlycomprises --CF₃ groups. The --CF₃ groups, which provide extremelyhydrophobic properties, prevent liquids and samples contained in thevessel from infiltrating the exposed coating and reacting with theintermediate carbon groups and linkage groups of the polymerizedmonomer. Such infiltration is particularly prevented when the coatingconsists of monomers of substantially uniform length of greater than 6carbon atoms, rather than a mixture of monomers of substantiallydifferent lengths.

According to embodiments of the invention, a polymer coating formed froma fluoroalkyl methacrylate monomer which has the chemical formula C₇ F₁₅CH₂ OCOC(CH₃)═CH₂ is provided. Coatings made with the polymerizedproduct of this monomer or similar fluoroalkyl monomers having atrifluoromethyl group, have exposed coating surfaces comprising tightlypacked terminal --CF₃ groups. The resultant coating has a low surfaceenergy, or critical surface tension, which can be as low as about 6dynes/cm at 20° C. depending upon the population of trifluoromethylgroups on the exposed surface and depending upon the material of thevessel which is coated. However, when a surface population of 100% byarea trifluoromethyl groups is achieved, the vessel material isirrelevant to the hydrophobicity of the surface.

As the packing of terminal trifluoromethyl groups increases, the surfaceenergy of the packed surface decreases, such that coatings having thelowest critical surface tension have the closest packed --CF₃ groups.The replacement of a single fluorine atom by a hydrogen atom in eachterminal trifluoromethyl group of such a surface would more than doublethe critical surface tension. of the surface. Critical surface tensionsof teflon vessels and teflon coated vessels are only as low as about 18dynes/cm at 20° C. because such surfaces mainly comprise --CF₂ --groups. Although it is difficult to obtain an exposed surface entirelycomposed of tightly packed --CF₃ groups, extremely low surface tensionscan be achieved by the formation of exposed coating surfaces whichcontain 30% or more, by surface area, --CF₃ groups. Preferably, anexposed surface having 50% or more --CF₃ groups can be achievedaccording to the processes of the present invention. These processestend to result in coatings having critical surface tensions ranging fromabout 6 dynes/cm to about 22 dynes/cm when formed on hydrophobic vesselmaterials.

Critical surface tensions, also referred to as surface energies, of aslow as about 6 dynes/cm can be obtained according to the processes ofthe present invention, depending upon which terminal trifluoromethylgroup-containing polymer or mixture of polymers is used to form thehydrophobic coating, the population of trifluoromethyl groups on theexposed surface, and the material of the vessel to be coated. Accordingto embodiments of the invention wherein the exposed surface area of thehydrophobic coating material is populated with from about 50% by area toabout 100% by area trifluoromethyl groups, surface energies of about 10dynes/cm or less can be provided, particularly if the coating is formedon a polypropylene or other substantially hydrophobic laboratory vesselmaterial, for example, a vessel material which exhibits a surface energyof 40 dynes/cm or less. Such surface energies are even lower than thoseof Teflon® which generally provides a surface energy of from about 18.5to about 20 dynes/cm. Although Teflon® is formed from polymerized fullyfluorinated monomers, most of the surface structure of a Teflon® coatingconsists of --CF₂ -- groups as opposed to closely packed terminaltrifluoromethyl (--CF₃) groups. Even the most hydrophobic forms ofTeflon®, FEP Teflon® and PFA Teflon®, which comprise mixtures of fullyfluorinated polypropylene and polyethylene polymerized monomers, onlyprovide surface energies of about 16.5 dynes/cm. As with other forms ofTeflon®, the exposed surface of an FEP Teflon® coating consists mainlyof --CF₂ -- groups as opposed to closely packed terminal trifluoromethyl(--CF₃) groups. Teflon® and FEP Teflon®, are available from DuPontPolymer Products Department, Wilmington, Del.

According to the present invention, lower surface tensions are obtainedwhen the coating polymer comprises the polymerization product of aperfluoroalkyl monomer, when compared to coatings comprising the productof a partially non-fluorinated monomer. Substantially non-branchedfluoroalkyl and perfluoroalkyl ethylenically unsaturated monomers arepreferred for producing the coating polymers of the invention. Accordingto other embodiments, a methacrylate group is used as a preferredethylenically unsaturated monomer for making the polymeric coatingmaterial of the invention. Other monomers which can be used includesilicones, epoxies and urethanes. Other reactants which may be usedinclude anhydrides, amines, polyols, vinyls, vinyl ethers, and mixturesthereof. Polymers made from mixtures of acrylates and epoxies or ofacrylates and silicones are particularly preferred according to someembodiments of the invention. Polymeric coating materials comprisingurethane monomers and/or polymers are preferred for some applicationswherein a durable coating is needed.

According to embodiments of the present invention, articles can beprovided with a coating thereon comprised of a prepolymerizedfluoroalkyl, or preferably perfluoroalkyl, ethylenically unsaturatedmonomer having a terminal trifluoromethyl group. More particularly, thepresent invention relates to such a coating which consists essentiallyof a polymerization product of a fluoroalkyl or perfluoroalkylethylenically unsaturated monomer having a terminal trifluoromethylgroup and an average carbon atom chain length of from 3 to about 20atoms, more preferably from about 6 to about 14 atoms, and optionally adurable resinous component such as a urethane or polyurethane component.

According to a preferred embodiment of the present invention,prepolymerized terminal trifluoromethyl-containing monomers having auniform pendant group length of from 8 to 10 carbon atoms andsubstantially free of branching can be deposited on laboratory vesselsto form coatings with low surface energies and critical surface tensionsof about 10 dynes/cm or less. The coatings also exhibit exceptionalresistance to many solvents with the exception of substantiallyfluorinated solvents. Coating solutions containing polymers of suchmonomers produce a highly ordered, densely packed polymer with apredominantly trifluoromethyl surface.

Solutions of polymers made from monomers having terminal trifluoromethylgroups are commercially available. One solution which can be used toform polymeric hydrophobic coatings according to the invention isavailable from The 3M Company as FC-722. Other trifluoromethylgroup-containing polymer solutions in fluorosolvents are available fromCytonix Corporation of Beltsville, Md. as the PerFluoroCoat andFluoroPel products lines. The coating solutions used according toembodiments of the present invention comprise fluoropolymers havingterminal trifluoromethyl groups. The solutions can be used full strengthbut may be diluted with a fluorosolvent to form low concentrations ofcoating polymer. The polymer solution used to make the coatings of theinvention preferably have a coating polymer content of from about 0.01%by weight to about 50% by weight.

Methods of making fluoropolymer coating solutions or suspensions for usewith the invention comprise prepolymerizing a fluoroalkyl ethylenicallyunsaturated monomer having a terminal trifluoromethyl group to form apolyfluoroalkyl polymer, and dissolving or suspending the polymer in afluorinated solvent. When making such solutions, the fluoroalkylethylenically unsaturated monomer preferably has a carbon chain lengthof from about 3 to about to 20 carbon atoms, with carbon chain lengthsof from about 6 to about 12 atoms being more preferred. Carbon chainlengths of from 8 to 10 atoms are particularly preferred. Mixtures ofdifferent fluoroalkyl ethylenically unsaturated monomers havingdifferent carbon chain lengths may be employed, however, when thepolymerized monomers have essentially uniform carbon chain lengths,hydrophobic coatings of extremely low and repeatable surface tension canbe provided.

According to embodiments of the invention, hydrophobic coatings areprovided which may preferably comprise, and more preferably consistessentially of, a polymerization product of a substantially non-branchedperfluoroalkyl monomer. Coatings according to the invention may comprisepolymerized products of monomers having terminal trifluoromethyl groups,including fluorinated or perfluorinated monomers such as hexylethylenically unsaturated monomers, heptyl ethylenically unsaturatedmonomers, octyl ethylenically unsaturated monomers, nonyl ethylenicallyunsaturated monomers, decyl ethylenically unsaturated monomers, undecylethylenically unsaturated monomers, and dodecyl ethylenicallyunsaturated monomers. Mixtures of two or more different monomers mayalso be used and are preferred when it is desired to adjust surfaceenergy properties to precise values.

The coatings of the present invention may comprise or consistessentially of a polymerization product of a fluoroalkyl ethylenicallyunsaturated monomer having a terminal trifluoromethyl group and a carbonchain length of from 3 to 20 atoms, preferably from 6 to 12 carbon atomsin length, and more preferably from 8 to 10 carbon atoms in length. Inparticular, polymerization products of fluoroalkyl methacrylates arepreferred. According to some embodiments of the invention,polymerization products of perfluorohexyl methacrylate, perfluoroheptylmethacrylate, perfluorooctyl methacrylate, perfluorononyl perfluorodecylmethacrylate, perfluoroundecyl methacrylate or perfluorododecylmethacrylate, and mixtures thereof, are preferred. Acrylates of suchperfluoroalkyls are also preferred. According to one particularlypreferred embodiment, the polymer coating consists essentially of apolymerization product of perfluorooctyl methacrylate.

Exemplary materials for making the coatings of the present inventioninclude PerFluoroCoat and FluoroPel, both available from CytonixCorporation, the fluorinated materials FC-722, FX-13, FX-14, FX-189,L-9187, L-9186, Fluorel™ FC 2174 and Fluorel™ FC 2181, all availablefrom Commercial Chemicals Division/3M, St Paul, Minn., silasticfluorosilicone rubbers from Dow Corning STI identified as LS-2249U,LS-2332U, LS-2840 and LS-2860, and fluorinated materials from DuPontincluding materials traded under the name ZONYL.

The solvent for the coating solutions used according to the inventionmay comprise a fully fluorinated non-branched fluorocarbon having acarbon chain length of 7 or 8 carbon atoms. Such a solvent exhibits aboiling point of about 80° C. Perfluorinated fluorocarbon solvents arepreferred according to some embodiments of the invention.

According to embodiments of the invention, preferred fluorinatedsolvents include the Fluorinert® line of fluorinated solvents, FC-71,FC-75, FC-40, FC-70, FC-77 and FC-84, all from the 3M Company. Otherfluorinated solvents which may be used include Vertrel® XF (C₅ H₂ F₁₀)or Freon TF from DuPont, Wilmington, Del., the fluorinated polyethersHT70, HT85, HT90, HT100, HT110, HT135, HT200, HT230, HT250 and HT270,and the perfluorinated polyethers sold as GALDEN, all from Ausimont USA,Inc. The Ausimont USA, Inc. solvent designations indicate the boilingpoint of each solvent. Higher boiling solvents, for example, HT270 andHT250, would form coatings requiring more heat to dry than coatings madewith the lower boiling solvents, for example, HT70. The lower boilingAusimont USA, Inc. solvents more rapidly evaporate when compared to thehigher boiling solvents.

Other fluorocarbon solvents may be used and typically have boilingranges of from about 30° C. to about 250° C., depending upon a number offactors including the length of the carbon chain. At least partiallyfluorinated solvents are preferred, particularly those fluorocarbonsolvents having at least about 20% by weight fluorine atoms permolecule. Solvents exhibiting surface energies of 18 dynes/cm or lowerare preferred, with solvents having surface energies of 13 dynes/cm orlower being more preferred and those having 9 dynes/cm being even morepreferred. In preferred embodiments of the methods of the presentinvention, the solvent is substantially recovered after a coatingprocedure. Volatile fluorinated surfactants may be included in thecoating formulations of the present invention.

Additives may be incorporated into or polymerized with the coatingpolymers and monomers used to provide coatings according to theinvention having improved toughness, chemical resistance, hardness,softness, processability, elasticity, adhesion, color, texture,thickness and/or uv-resistance. Hydrophobic additives are preferred.Chemically resistant additives are preferred. Additives includingnon-trifluoromethyl-containing reactants and/or monomers may be added inamounts ranging from 1 to about 95% by weight and are described in moredetail below.

According to an embodiment of the present invention, extremelyhydrophobic surfaces on a variety of articles not limited to laboratoryvessels can be formed. The compositions of the present invention areuseful for any article which is intended to be exposed to elements, thatis, exposed to the environment, exposed to precipitation, unprotected,unsheltered. The compositions of the present invention provide surfacesthat are preferably weatherable, rust resistant, corrosion resistant,able to maintain the appearance of a surface, able to withstand contactwith precipitation without degradation, chemically resistant andmechanically resilient. Compositions are provided that combinerelatively soft polymers of unbranched trifluoromethyl-containingmonomers, and tough, chemically resistant non-fluorinated resins such asacrylics, cellulosics, epoxy, polyesters, silicones, urethanes,anhydrides, amines, polyols, vinyls, vinyl ethers, and combinationsthereof. These mixtures may produce surfaces that are rich intrifluoromethyl groups and interior compositions that are substantiallynon-fluorinated.

The coating compositions for articles not limited to laboratory vessels,according to the present invention, can include functionalizedfluoropolymers that have cross-linkable chemical groups, for example,Lumiflon® FE3000, FE4100, FE4200, FE4400, LF100, LF200, LF302, LF400,LF600X, LF710N, LF800, LF910LM, and LF916N, from Asahi Glass Co., Tokyo,Japan. The coating compositions of the present invention can includefluorourethanes, for example, those available from Century 2000Coatings, Alexandria, Va., and those disclosed in U.S. Pat. No.4,132,681 to Field, which is herein incorporated in its entirety byreference. Particularly preferred are fluorourethanes comprisingpolymers of polyisocyanates and fluorine-containing diols, resulting ingood chemical and mechanical properties. These fully or partiallyfluorinated resins may be used as primers for other coatings of thepresent invention or as mixtures with polymers and/or monomers accordingto the present invention.

The coating formulations for articles can produce extremely hydrophobicsubstantially unbranched highly populated trifluoromethyl surfaces andinterior compositions that are unfluorinated, partially fluorinated orperfluorinated. The phrase "highly populated" applies to surfacepopulations of 15% by area or greater trifluoromethyl groups.

The coating compositions for articles not limited to laboratory vessels,of the present invention, can comprise: a copolymer of at least onefluorine-containing monomer; a perfluoropolymer; tetrafluoroethylene;perfluoro-2,2-dimethyl-1,3-dioxole (PDD); fluoroethylenepropylene; apolymer containing difluoromethylene; a functionalized fluoropolymer;the polymerization product of a branched trifluoromethyl (TFM)containing monomer; or combinations thereof.

According to some embodiments of the present invention, the coatingcomposition for articles includes an aromatic or aliphatic polyurethane.According to some embodiments of the present invention, the coatingpreferably comprises the polymerization product of anisocyanate-containing monomer. Optionally, the coating can furthercomprise a cellulosic; a polyester; the polymerization product of anunsaturated monomer; a condensation polymer; a silicone polymer; anepoxy; or combinations thereof.

The present invention also provides a coated formed rough surface forarticles not limited to laboratory vessels. The coating comprises atleast one fluorinated component including a fluorinated monomer or apolymerization product thereof. The fluorinated monomer has from about 3to about 40 fluorine atoms and at least one trifluoromethyl group. Theformed rough surface has features smaller than about 100 microns. Thecoated surface provides a surface area populated with 30% by area ormore trifluoromethyl groups and a surface energy of about 22 dynes/cm orlower. The formed rough surface can comprise a pattern of features.

According to some embodiments of the invention, hydrophobic coatings aremade of a polymerization product of a fluorinated monomer having aterminal trifluoromethyl group, and further containing small amounts ofco-monomers, for example, silanes, that serve to promote adhesion tometal, glass or ceramic vessels without compromising the extremely lowsurface energy of the coating. Coupling agents may also be used asadhesion promoting monomers and include those listed in Table 1 underthe heading "Coupling Agents" in the Polymer Encyclopedia. Exemplarycoupling agents include vinyltrimethoxysilane,chloropropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and3-methacryloxypropyl-trimethoxysilane. Such silanes and coupling agents,if present, can be present in amounts of from 1% by weight to 10% byweight, more preferably from about 2% by weight to about 5% by weight.If co-monomer is added, the amount added is not so much as to cause thesurface population of trifluoromethyl groups to be less than 30% byarea.

Other adhesion promoting monomers can be added to the coatingformulations of the invention. If used, adhesion promoting monomersother than silanes are preferably added in amounts of from about 1% byweight to about 40% by weight, more preferably from about 5% by weightto about 20% by weight, based on the weight of the polymerizationproduct making up the coating material. Adhesion promoting monomerswhich may be used include alkoxy terminated monomers and methacrylateesters and acrylate esters listed as adhesion promoting monomers on page16 of the 1994 Sartomer Product Catalog, including mono-, di- andtrifunctional acrylate or methacrylate ester monomers.

Other additives which may be incorporated or polymerized with theterminal trifluoromethyl-containing monomers or products of theinventive coatings include high glass transition temperature (highT_(g)) perfluorinated or non-perfluorinated monomers, and low T_(g)perfluorinated or non-perfluorinated monomers. High T_(g) monomers canbe included to form hard hydrophobic coatings for laboratory vessels,which are highly resistant to solvent removal and retention ofbiological sample. Preferably, the coating composition comprises afluoropolymer having a T_(g) of greater than 100° C., more preferably,greater than 140° C. The hard coatings are harder than similar coatingswhich differ only in that they do not incorporate the high T_(g)component. High T_(g) monomers which may be employed include thosefluorochemical acrylate or methacrylate monomers which form homopolymersexhibiting T_(g) 's of 50° C. or higher. Exemplary additives of thiscategory are available from the 3M Company as FX-14 (homopolymer T_(g)=60° C.), L-9187 (homopolymer T_(g) =60° C.), and L-11913 (homopolymerT_(g) =116° C.). Of the exemplary monomers denoted above, L-11913 is apreferred monomer, and has the formula: cyclo-C₆ F₁₁ CH₂ OCOC(CH₃)═CH₂.If L-11913 is incorporated, it is preferably employed in an amount offrom about 1% by weight to about 60% by weight, based on the weight ofthe coating.

Low T_(g) monomers can be included to form soft, hydrophobic coatingsfor laboratory vessels, which are highly resistant to solvent removaland retention of biological sample. The soft coatings are softer thansimilar coatings which differ only in that they do not incorporate thelow T_(g) component. Low T_(g) additive monomers can be used to formhydrophobic pressure sensitive adhesive coatings, which find many usesincluding the ability to adhere to covering materials such as Teflontape or high T_(g) coatings of the present invention, even underwater.Low T_(g) monomers which may be employed include fluorochemical acrylateor methacrylate monomers which form homopolymers having T_(g) 's ofabout 5° C. or lower, preferably about 0° C. or lower. More preferredlow T_(g) monomers have terminal trifluoromethyl groups. Exemplaryadditives of this category are available from the 3M Company as FX-189(homopolymer T_(g) =3° C.), L-9186 (homopolymer T_(g) =0° C.), L-9911(homopolymer T_(g) =-53° C.), L-12044 (homopolymer T_(g) =-23° C.),L-12043 (homopolymer T_(g) =-5° C.), and L-9367 (homopolymer T_(g)=-120° C.). Of the foregoing monomers, L-9186 is a preferred monomer andhas the formula: C₇ F₁₅ CH₂ OCOCH═CH₂. Combinations of different lowT_(g) and high T_(g) monomers may be added to the coating formulationsof the present invention to provide the coating with a specific hardnessor pressure sensitive adhesiveness.

Other additives which may be added to the coating solutions of theinvention include perfluorinated and non-perfluorinated plasticizers.Plasticizers can be added in amounts of from about 1% by weight to about30% by weight, more preferably 5% by weight to about 10% by weight,based on the weight of the coating. Exemplary plasticizers include highboiling point Fluorinert solvents from the 3M Company including FC-71,and high boiling point perfluorinated polyethers available from AusimontUSA, Inc., including HT270.

Cross-linkable monomers may be incorporated into the coating solutions,suspensions and formulations according to embodiments of the presentinvention. Cross-linkable monomers may preferably be used for someapplications in amounts ranging from about 1% by weight to about 95% byweight, preferably from about 5% by weight to about 70% by weight, andeven more preferably from about 10% by weight to about 20% by weight.Cross-linkable monomers which may be incorporated include epoxies suchas novolac epoxies, bisphenol A epoxies, acrylates, silicones,urethanes, anhydrides, and silicates.

Reactive non-fluorinated monomers and resins can also be added to thecoating formulations of the invention to provide different properties tothe coatings. According to embodiments of the invention, reactivemonomers and resins such as methacrylate monomers, silicone monomers,epoxy monomers, urethane monomers and oximes can be included in thecoating formulations.

According to embodiments of the invention, coating formulations areprovided comprising epoxy monomer or resin in amounts of from about 20%by weight to about 95% by weight, based on the total weight of thecoating formulation. Preferably, from about 30% by weight to about 70%by weight epoxy monomer may be included in a curable coatingformulation. Epoxy resins may be used including the EPON Resins fromShell Chemical Company, Houston, Tex., for example, EPON Resins 1001F,1002F, 1007F and 1009F, as well as the 2000 series powdered EPON Resins,for example, EPON Resins 2002, 2003, 2004 and 2005. Preferably, theepoxy monomer or resin has a high crosslink density, a functionality ofabout 3 or greater, and an epoxy equivalent weight of less than 250.Exemplary epoxies which may be employed according to embodiments of theinvention include The Dow Chemical Company (Midland, Mich.) epoxynovolac resins D.E.N. 431, D.E.N. 438 and D.E.N. 439.

If an epoxy is included in the coating formulation, a curing agent forthe epoxy may be added in amounts of from about 1% by weight to about10% by weight of the epoxy component. The curing agent may be a catalystor a reactant, for example, the reactant dicyandiamide. From about 1% byweight to about 50% by weight epoxy solvent, based on the weight of thecoating formulation, may also be included in the coating formulations.Epoxy solvents can be added to liquify the epoxy monomer or resin oradjust the viscosity thereof. Preferred epoxy solvents aretriethylphosphate and ethylene glycol. A separate epoxy solvent may notbe needed according to some embodiments of the invention wherein theepoxy is liquid at room temperature or wherein a fluorinated monomer orsurfactant component of the coating formulation acts as a solvent forthe epoxy.

Even when a large amount of non-fluorinated epoxy is included in acoating formulation according to the invention, surface populations oftrifluoromethyl groups of about 30% by area or more can nonetheless beachieved on the coating. Prepolymerized trifluoromethyl-containingmonomers and/or reactive trifluoromethyl-containing monomers in thecoating formulation tend to migrate to the surface of the coating duringheat curing of the epoxy. The trifluoromethyl-containing components aremobile during epoxy curing due to thermal forces, convective forces,evaporative forces and diffusion forces. If included in a formulation,volatile trifluoromethyl-containing monomer is mostly driven off duringheat curing of the epoxy, but can be polymerized into the coating in thepresence of peroxide or azo compound catalysts, initiators or promoters.

According to some embodiments of the invention, the coating formulationcomprises an aqueous suspension of the trifluoromethyl-containingcomponent such as ZONYL NWA, from DuPont. Suspension formulationsaccording to the invention, may further include additives as discussedabove, including epoxy resins. Exemplary waterborne epoxy resins whichmay be used in aqueous suspension coating formulations according to theinvention include the EPI-REZ Resins from Shell Chemical Company, forexample, the EPI-REZ Resins WD-510, WD-511, WD-512, 3510-W-60,3515-W-60, 3519-W-50, 3520-WY-55 and 3522-W-60. The coating compositionmay comprise microparticles, microfibers, foaming and/or pore-formingagents, and may be dried, cured, and/or hardened so as to producesufficient surface roughness to provide high contact angles to water.

According to some embodiments of the invention, a coating solution orsuspension is provided which comprises prepolymerized fluorinatedmonomer, reactive non-polymerized fluorinated monomer, and an additionaladditive, for example, at least one of the additives discussed above.The additional additive may be added in substantial amounts, forexample, up to 95% by weight, provided the resultant coating has asurface population of trifluoromethyl groups which is about 30% by areaor more. Preferably, coating techniques which involve application of asolution containing unreacted monomer further include a step ofrecovering unreacted monomer after coating.

According to some embodiments of the invention, an operational surfaceof a laboratory vessel is at least partially coated withtrifluoromethyl-containing monomers and non-trifluoromethyl-containingmonomers followed by polymerization of the monomers and removal andrecovery of unreacted monomers. According to some embodiments, themonomers are applied from a coating solution which further includes afluorinated solvent. Preferably, when reactive fluorinated monomers areused to coat an operational surface, and subsequently polymerized,unreacted monomer is removed and substantially recovered after coatingand curing.

According to some embodiments of the invention, the coating solutioncomprises the polymerization product of substantially terminaltrifluoromethyl-containing monomers, and unreacted terminaltrifluoromethyl-containing monomers. After coating an operationalsurface, the coating is then subsequently polymerized to form polymerfrom the unreacted monomer in the coating solution. Such a procedureresults in extremely hydrophobic coatings. When partially unreactedcoating solutions are used, they may also include from about 15% byweight to about 95% by weight, based on the weight of the coating, ofnon-perfluorinated functional monomer, such as an epoxy.

Linkage mechanisms for binding the trifluoromethyl-containing monomer orpolymer of the present coating formulations to an operational surface ofa vessel include functional linkage groups such as peroxide catalyzedlinkages, azo catalyzed linkages, free radical induced linkages,cationically induced linkages, radiation induced linkages, vinyllinkages, methacrylate linkages, urethane linkages, epoxy linkages,condensation linkages, silane linkages, and siloxane linkages.

According to embodiments of the invention, prepolymerized hydrophobiccoatings according to the invention comprise a polymerization product ofa substantially trifluoromethyl-containing monomer, that is, having atleast about 15%, preferably 30%, of the terminal groups of the reactantmonomer or monomers comprising trifluoromethyl groups, and from about 1%by weight to about 10% by weight of additional comonomers. Theadditional comonomers having functionality that is polymerizable by asecond, different mechanism than the mechanism used to polymerize thesubstantially trifluoromethyl-containing monomer. The secondpolymerization mechanism may be activated during or followingapplication of the hydrophobic coating to an operational surface,allowing the hydrophobic coating to become crosslinked with itself orwith the vessel walls. For example, the initial polymerization may becarried out as an addition reaction of acrylates or methacrylates usinga free radical catalyst, whereas the second polymerization may becarried out as a cationic reaction of epoxides using a cationic or acidcatalyst. An exemplary material having epoxy functionality and acrylatefunctionality is glycidyl-methacrylate. Peroxides will attachhydrocarbon groups to hydrocarbons on the surface of the vessel.

According to some embodiments of the invention, low surface energies canbe obtained when a terminal trifluoromethyl-containing monomer is coatedonto the operational surface of a vessel and subsequently polymerizedafter coating. Substantially non-branched fluoroalkyl and perfluoroalkylethylenically unsaturated monomers are preferred according toembodiments of the invention. According to some embodiments, amethacrylate group is used as the preferred ethylenically unsaturatedmonomer. Other monomers which can be used include fluorinated orperfluorinated silicones, epoxies, urethanes and oximes. Polymers madefrom mixtures of acrylates, urethanes and epoxies are particularlypreferred. According to some embodiments, both prepolymerizedfluorinated monomer and reactive non-polymerized fluorinated monomer areused in the coating formulation, and after application to an operationalsurface, the reactive monomer is then polymerized or volatilized.Preferably, the reactive monomer is polymerized.

Another method of forming a coating according to embodiments of theinvention is by using monomers capable of free radical linkages. Suchmonomers can be attached to vessel surfaces if the vessel surfaces arefirst treated by ionizing radiation or other means to generate freeradicals across the surface. A monomer capable of free radical linkagescan be formed by mixing a fluoroalkyl ethylenically unsaturated monomerdissolved in a suitable fluorocarbon solvent with an effective amount ofa free radical initiator. Vessels coated with the mixture are thenheated to the temperature at which the free radical initiator initiatesfree radical generation. Many conventional azo compounds have anappropriate activation temperature, particularly within the range of30-200° C. Many azo compounds may be used which are activated by visibleor ultraviolet light.

According to some embodiments of the invention, when working withliquids which only slightly wet fluorinated surfaces, for example, whenthe contact angle between the liquid and the surface is greater than90°, it may be desirable to provide a rough surface coating on alaboratory vessel to more effectively prevent runoff of the liquid asmight occur from a smooth hydrophobic coating. Such would be theobjective when it is desired to maintain a drop of liquid sample on amicroscope slide. A microscopically roughened or porous hydrophobicsurface which will not be wetted can be made according to the presentinvention by adding microscopic particles of a surface roughening agent,for example, a micropowder, to the hydrophobic coating material or tothe surface to which the coating polymer is to be applied. According toembodiments of the invention, microscopic particles can be added tocoating formulations of the present invention which comprise (1) apolymerization product of a trifluoromethyl-containing monomer, (2) anunreacted trifluoromethyl-containing monomer, or both (1) and (2).Microscopic particles can also be added to coating formulations whichfurther include a fluorinated solvent.

While many microparticles may be used as surface roughening agentsaccording to the present invention, micropowders are a preferred classof surface roughening agents. Micropowders are defined herein as thosepowders or particles having average diameters of from submicron sizes upto 100 microns. A preferred micropowder average diameter is about 10microns or less. Hydrophobic materials are particularly preferred forthe micropowders. Suitable micropowders include silicon glass particleswith and without silane coatings, pigments, Teflon® powders, flour,cornstarch, siliconized glass, fluorosiliconized inorganic pigments, andmicronized cellulosics. According to embodiments of the invention, acomposite surface is formed by adding a substantially uniformly sizedmicropowder to a fluoropolymer or a fluoromonomer which is to besubsequently coated and then polymerized. The use of micropowdersexhibiting wide particle size distributions also provides preferredcoatings according to some embodiments of the present invention.

Inert micropowders are preferred, particularly for applications wherethe resultant coating is exposed to liquids which are other than aqueousin nature. One particularly preferred micropowder is a siliconized glassparticulate material having a 0.3 micron average particle size diameteravailable as TULLANOX HM 250 or TULLANOX HM 250D, from Tulco, Inc.,Ayer, Mass. Another preferred micropowder is Teflon® MP 1200, availablefrom DuPont Polymer Products Department, Wilmington, Del., and having anaverage particle diameter of about 4 μm.

Microfibers are another class of surface roughening agents and may beused in the coating compositions of the present invention. Inertmicrofibers are preferred according to some embodiments of theinvention, for example, some embodiments requiring mechanical strength.A preferred microfiber is a cellulose microfiber having an averagediameter of about 4 microns and an average length of about 40 microns,for example, TECHNOCELL 40™ available from EastTec, of Pennsylvania.Microfibers of longer lengths are also preferred.

The methods of the present invention may comprise diluting atrifluoromethyl-containing coating polymer solution or suspension priorto applying the solution or suspension to an operational surface of alaboratory vessel. The coating solution or suspension is preferablydiluted to between about 0.01 and 2 percent by weight coating polymer.Higher weight percentages of the polymer may be used although higherconcentrations tend to clog small orifices such as the opening at theend of a pipette tip for a volumetric pipettor, or small orifices suchas nozzles and nozzle openings in ink jet printer print heads.

One preferred method for applying a coating polymer solution orsuspension comprises dip-coating a laboratory vessel or other articlesinto a polymer solution or suspension. Other coating methods may also beused, including spray coating, tumbling in solution, brush coating,padding, spraying, fogging, transferring, painting, printing,stenciling, screen printing, pad printing, ink jet printing, injectionmolding, laminating and doctoring. For articles having interior wallsdefining a reservoir portion, the area of the article around anddefining an opening to the reservoir is preferably also coated. Forsimultaneously coating a large number of small articles, each having areservoir portion, a tumbling method of coating is preferred.

Dip coating may be used according to some embodiments of the inventionto apply the coating polymer from a solution of the polymer dissolved ina fluorosolvent or from a suspension of the polymer. After coating thepolymer solution, the coating is allowed to dry and solvent or carrieris driven off.

After forming a first coating of polymer according to the invention, themethods of the invention may also comprise applying at least one othercoating formulation comprising a polymer having terminal trifluoromethylgroups. According to some embodiments of the invention, one or morecoatings of the same or different terminal trifluoromethyl-containingpolymers may be applied, depending upon the desired surface energyproperties of an operational surface being coated.

According to some embodiments of the invention, the coating formulationis not a polymer solution or suspension but instead comprises afluidized micropowder of the polymerization product of entirely orsubstantially trifluoromethyl-containing monomers. The micropowderformulation can be applied to at least a portion of an article surface,for example, an operational surface of a laboratory vessel, and meltedto form a hydrophobic coating having an extremely low surface energy, ahigh resistance to solvent removal, and for laboratory vessels, a lowretention of biological samples. According to some embodiments, thecoating formulation comprises a fluidized micropowder of thepolymerization product of entirely or substantiallytrifluoromethyl-containing monomers, and at least one substantiallynon-perfluorinated resin. The micropowder and resin are applied to asurface, for example, an operational surface of a laboratory vessel andheated to melt the fluidized micropowder.

According to embodiments of the invention, the coating polymer orcoating monomer formulation of the invention is applied as a micropowderalong with at least one of a curable resin and a non-curable resin.Preferably, the at least one resin is substantially non-perfluorinated.Curable resins which can be used in formulations of micropowder coatingmaterial include epoxy resins, urethane resins, acrylate resins,methacrylate resins. Highly cross-linked resins provide excellentsolvent resistance according to embodiments of the invention. Anexemplary resin having a high crosslink density is the epoxy novolacresin D.E.N. 439, available from Dow Chemical Co., Midland, Mich.

According to other embodiments, resins with low cross-link densities maybe employed for coatings subsequently used with aqueous mediums. Anexemplary low crosslink density resin is the fusion solid EPON Resin1004F available from Shell Chemical Company, Houston, Tex. EPON Resin1004F is a bisphenol A epoxy resin having a melting point of about 100°C. Other EPON Resins from Shell Chemical Company may also be used,including 1001F, 1002F, 1007F and 1009F, as well as the 2000 seriespowdered EPON Resins, for example, EPON Resins 2002, 2003, 2004 and2005.

Non-curable resins which may be employed include powdered ethylcellulose, powdered polyethylene, powdered polypropylene and powderedpolyvinylidenedifluoride. Cellulose acetate butyrate pellets also be jetmilled and applied as a powder. Cellulose acetate butyrate is typicallynon-curable but can be cross-linked with peroxides.

The substantially non-perfluorinated resin is preferably non-fluorinatedaccording to some embodiments of the invention.

The micropowders and resins used according to embodiments of theinvention can be formed, for example, by jet milling. The micropowdersand resins are preferably particles having an average diameter of about50 microns or less, with average diameters of 10 microns or less beingmore preferred. The powders can be electrostatically sprayed onto asurface with or without a curing agent.

Micropowders according to the present invention may also be prepared aslatexes in aqueous suspensions, subsequently separated from the liquidphase, and dried. Nanopowders and micropowders with substantiallytrifluoromethyl surfaces may be prepared in radio frequency andmicrowave plasmas of trifluoromethyl-containing gases.

In another embodiment of the invention, the coating is formed from afluidized micropowder product of trifluoromethyl-containing monomer andsubstantially non-perfluorinated resin, wherein the micropowder isapplied and melted on an operational surface.

In another embodiment of the invention, a fluidized micropowder of anon-perfluorinated resin is coated with the polymerization product of asubstantially trifluoromethyl-containing monomer. The powder issubsequently melted to form a hydrophobic coating.

In another embodiment of the invention, a surface is coated with acoating formulation comprising a fluidized micropowder of apolymerization product of substantially trifluoromethyl-containingmonomer, and a hydrophobic non-melting micropowder that does not melt attemperatures required for formation of the coating. The formulation isthen heated or sintered to melt the fluidized polymerization productmicropowder without melting the non-melting micropowder. The non-meltingmicropowder is preferably selected from the group consisting of Teflonmicropowders, Tefzel™ micropowders, Kynar™ micropowders, polyvinylidenedifluoride micropowders, and polypropylene micropowders.

According to embodiments of the invention which involve forming coatingsby melting micropowders, the coating formulations may be applied as asuspension to the operational surface and subsequently dried prior tomelting.

Another method of forming laboratory vessels having hydrophobic coatingsaccording to the present invention involves preinjecting or coinjectinga coating formulation prior to or during the laminar flow of moltenmaterials injected into a mold or through an orifice to form articles,for example, laboratory vessels. The coating formulation comprises theprepolymerization product of a trifluoromethyl-containing monomer,preferably a product which has from about 50% to 100% of exposedterminal groups being trifluoromethyl groups. The preinjected orcoinjected coating formulation may also comprise a thermoplastic resinand/or a thermosetting resin. The injectable coating formulation maycomprise mixtures of trifluoromethyl-containing monomer, catalyst, andresin. The injectable coating formulation may comprise mixtures ofmolten prepolymerized trifluoromethyl-containing monomer andmicroparticles, to form coatings exhibiting extraordinarily high contactangles of 160° or more to aqueous liquids. The injectable coatingformulations may comprise mixtures of molten prepolymerized entirely oressentially trifluoromethyl-containing monomers, other resins, andmicroparticles, which are preinjected or coinjected to or during thelaminar flow of molten materials injected into a mold or through anorifice to form coatings on the resultant vessels having extraordinarilyhigh contact angles to aqueous liquids, high resistance to solventremoval, and low retention of biological samples.

According to yet other embodiments of the invention, a tubularlaboratory vessel such as a microcentrifuge tube or test tube isprovided and comprises a tubular body having an interior sidewall and aclosed lower end having an interior surface. A hydrophobic coatingaccording to the invention is applied to the interior sidewall but notto the interior surface of the closed lower end, or the interior closedend is substantially free of the coating. An aqueous sample placed inthe tubular body tends to be retained at the closed lower end of thevessel and tends not to creep or advance onto the coated interiorsidewall, even during movement of the vessel.

Other applications of the coating compositions of the present inventioninclude their use on ink-jet ink print heads to form hydrophobicsurfaces surrounding ink jet nozzle orifices. Hydrophobic properties insuch regions of an ink jet print head are particularly beneficial in theuse of organic solvent based ink jet inks which have even a greatertendency to wet-out on the print head than do aqueous based ink jetinks. The hydrophobic nature of such a print head design prevents nozzleclogging and cross-contamination between individual orifices of theprint head. The entire print head surface containing the ink jet nozzleorifices can be coated with the hydrophobic coating composition of thepresent invention or only in areas surrounding the individual orifices.The compositions for such uses can may or may not contain a hardenablematerial along with the trifluoromethyl-containing component.

The present invention is exemplified with reference to the followingExamples. In the Examples below, the surface energies of the coatingswas determined as follows. A series of hydrocarbon oils with knownsurface tensions were used to develop a graph of liquid surface tensionsverse the cosines of the liquid contact angles for each oil. Theinterpolated intercept of the graphed line at a cosine of one indicatesthe surface energy of the coating.

EXAMPLE 1

A plurality of polypropylene pipette tips were enclosed in amonofilament polyester mesh bag and the bag was placed in a tumbling oragitating device. The mesh bag permitted treatment of the pipette tipsby allowing coating solution to pass through the bag and substantiallywet the surfaces of the pipette tip, including surfaces at and aroundthe tip openings. The tumbling device was fitted with special gaskets torender the machine interior air-tight and fluid-tight. To the machineinterior was also added a sufficient amount of coating solution to atleast partially immerse the bag of pipette tips. The coating solutioncomprised a diluted solution of a fluorocarbon polymer having terminaltrifluoromethyl groups. The fluorocarbon polymer solution is availableas FluoroPel from Cytonix Corporation. The FluoroPel solution providesthe polymer completely dissolved in a fully fluorinated solvent ofperfluorinated fluorocarbons having an average carbon chain length offrom about 7 to about 8 carbon atoms. The solvent exhibited a boilingpoint of from about 90° C. to about 100° C. Additional perfluorinatedsolvent or similar perfluorinated fluorocarbon solvent was added as adiluent to the FluoroPel solution to provide a coating solution having asolids content of coating polymer of about 0.5% by weight.

The tumbling device was equipped with a blower for removing volatilesolvent from the coating and interior airspace, and with a heater forheating air to be blown by the blower. The tumbling device was run toagitate and tumble the pipette tips and the coating solution, thusevenly distributing the coating solution on the surfaces of the tips andsufficiently wetting the surfaces of the tips, including surfaces at oraround the tip openings. The interior of the device was maintained at orbelow room temperature during solution coating of the tips. After a fewminutes of tumbling, a drain in the interior of the device was opened toallow excess coating solution to drain out from the tumbling deviceinterior during further tumbling. After a few minutes of draining withcontinued tumbling, the blower and heater were turned on and air havinga temperature of about 80° C. was blown through the device interior, andexhausted. The heated air evaporated solvent from the coated solutionand from the interior airspace of the tumbling device. The bag ofpipette tips continued to tumble during the drying process. The drainedand evaporated solution and solvent was collected, reconcentrated andrecycled. The coating polymer was not volatile under exposure to the 80°C. air.

The coated and dried pipette tips were removed from the device interiorand mesh bag. Both exterior and interior surfaces of the tips werecoated by the process. The coated surfaces had a resultant surfaceenergy of less than about 10 dynes/cm and an estimated surfacepopulation of trifluoromethyl groups of about 50% by area or more.

EXAMPLE 2

A highly chemically and solvent resistant hydrophobic coating for amicroscope slide was prepared. The coating was provided from a coatingformulation having the following ingredients:

50 parts by weight high functionality novolac epoxy resin, available asD.E.N. 439 from The Dow Chemical Company, Midland, Mich., having anepoxy functionality of 3.9, an epoxy equivalent weight of about 220, anda high cross-link density;

8% by weight dicyandiamide as a reactant agent for curing the epoxy,based on the weight of the epoxy;

50 parts by weight calcinated pigment;

10 parts by weight epoxy solvent triethylphosphate to liquify and reducethe viscosity of the epoxy;

10 parts by weight trifluoromethyl-containing polymer, comprisingPerFluoroCoat (PFC) 468MP (a solution of polymerized and non-polymerizedperfluoroalkyl monomers) available from Cytonix Corporation; and

1 part by weight 3-glycidoxypropyltrimethoxysilane.

The coating formulation was mixed, screen printed on a microscope slide,heat cured and allowed to dry. The resultant cured and dried coatingexhibited a contact angle to water of 120°, was very hard, could not bescratched with a #8H pencil, and was chemically resistant to removal ina plurality of common lab solvents including acetone, water, chloroform,trichloroethane and trifluoroethane, at 20° C. The coating exhibited avery low surface energy, and the population of trifluoromethyl groups onthe exposed surface of the coating exceeded 80% by area as determined bysurface energy analysis.

EXAMPLE 3

A composite hydrophobic coating was prepared and provides a roughsurface upon curing. The coating can exhibit extremely high contactangles to water. The coating was prepared as follows:

50 parts by weight D.E.N. 438 epoxy, 70 parts by weighttriethylphosphate, 4 parts by weight dicyandiamide, and 1 part by weight3-glycidoxypropyltrimethoxysilane were thoroughly mixed together. Then,50 parts by weight TiO₂ having an average particle size diameter ofabout 1 μm was added and the mixture was again mixed thoroughly. Then,100 parts by weight Teflon® MP 1200 powder was added and the mixture wasagain mixed thoroughly. Then, 100 parts by weight Teflon® MP 1200 powderwas added and the mixture was again mixed thoroughly. Then, 10 parts byweight PFC 468MP was added and the mixture was again mixed thoroughly.The resulting formulation was applied to an operational surface of alaboratory vessel and allowed to cure for 3 minutes at 200° C.

EXAMPLE 4

A composite hydrophobic coating was prepared and provides a roughsurface upon curing. The coating can exhibit extremely high contactangles to water. The coating was prepared as follows:

90 parts by weight Shell 1004-QX-55 (bis-A epoxy in xylene and propyleneglycol monomethyl ether acetate), 1 part by weight imidizol (optional),40 parts by weight ethylene glycol, and 10 parts by weight organicpigment were thoroughly mixed together. Then, 10 parts by weightTullanox glass micropowder was added and the mixture was again mixedthoroughly. Then, 10 parts by weight PFC 468TF (solution ofperfluoroalkyl polymer in Freon TF), available from Cytonix Corporation,was added and the mixture was again mixed thoroughly. The resultingformulation was applied to an operational surface of a laboratory vesseland allowed to dry at room temperature for 24 hours.

EXAMPLE 5

A highly chemical and solvent resistant hydrophobic coating for sprayingor dipping was prepared. The coating was provided from a coatingformulation having the following ingredients:

Part A

5 parts Futurathane 660 part A (Futura Coatings, Inc.-USA)

5 parts acetophenone (Aldrich Chemical)

20 parts Vertrel MCA

Part B

33 parts Vertrel MCA (Dupont)

10 parts Asakalin 225 (Asahi Glass)

0.5 part 9187 polymer (Cytonix)

1.5 parts 9187 monomer (3M)

15 parts Futurathane 660 part B (Futura Coatings, Inc.-USA)

Parts A and B were mixed and sprayed onto glass, plastic and metalarticles and allowed to dry and cure under ambient conditions for 72hours. The resultant coatings were scratch resistant to a #6 pencil, hada contact angle to water of 120°, and were not altered by acetone,toluene or chloroethane. The population of trifluoromethyl groups at thesurface exceeded 80 percent

EXAMPLE 6

A highly chemical and solvent resistant hydrophobic coating for sprayingor dipping was prepared. The coating was provided from a coatingformulation having the following ingredients:

Part A

5 parts Futurathane 660 part A (Futura Coatings, Inc.-USA)

5 parts acetophenone (Aldrich Chemical)

20 parts Vertrel MCA

24 parts Zonyl 1300 micropowder (Dupont)

Part B

33 parts Vertrel MCA (Dupont)

10 parts Asakalin 225 (Asahi Glass)

0.5 parts 9187 polymer (Cytonix)

1.5 parts 9187 monomer (3M)

15 parts Futurathane 660 part B (Futura Coatings, Inc.-USA)

Parts A and B were mixed and sprayed onto glass, plastic and metalarticles and allowed to dry and cure under ambient conditions for 72hours. The resultant coatings had a contact angle to water of 150°, andwere not altered by acetone, toluene or chloroethane. The population oftrifluoromethyl groups at the surface exceeded 80 percent.

EXAMPLE 7

A highly hydrophobic coating composition for spraying or dipping wasprepared. A coating was provided from the coating formulation which hadthe following ingredients:

100 parts Asakalin 225 (Asahi Glass)

5 parts 9187 polymer (Cytonix)

25 parts 9187 monomer (3M)

100 parts HelmsMan Spar Urethane (Minwax, Upper Saddle River, N.J.)

Ingredients were mixed and sprayed onto glass, plastic and metalarticles and allowed to dry and cure under ambient conditions for 24hours. The resultant coatings were scratch resistant to a #2 pencil andhad a contact angle to water of 120°.

EXAMPLE 8

A highly hydrophobic coating for spraying or dipping was prepared. thecoating was provided from a coating formulation having the followingingredients:

200 parts Asakalin 225 (Asahi Glass)

5 parts 9187 polymer (Cytonix)

25 parts 9187 monomer (3M)

120 parts Zonyl 1300 micropowder

100 parts HelmsMan Spar Urethane (Minwax, Upper Saddle River, N.J.)

Ingredients were mixed and sprayed onto glass, plastic and metalarticles and allowed to dry and cure under ambient conditions for 24hours. The resultant coatings had a contact angle to water of 150°.

EXAMPLE 9

A highly hydrophobic coating for spraying or dipping was prepared. Thecoating was provided from a coating formulation having the followingingredients:

200 parts Asakalin 225 (Asahi Glass)

5 parts 9187 polymer (Cytonix)

25 parts 9187 monomer (3M)

80 parts TechnoCel® 40 (available from Cellulose Filler Factory,Chestertown, Md.)

100 parts HelmsMan Spar Urethane (available from Minwax, Upper SaddleRiver, N.J.)

The ingredients were mixed and sprayed onto glass, plastic and metalarticles and allowed to dry and cure under ambient conditions for 24hours. The resultant coatings had a contact angle to water of 150°.

EXAMPLE 10

A highly hydrophobic coating for printing or painting was prepared. Thecoating was provided from a coating formulation having the followingingredients:

100 parts by weight N68 from Norland

10 parts by weight Asakalin 225 from Asahi Glass

10 parts by weight Zonyl TA-N from DuPont

The ingredients were mixed and painted onto glass, plastic and metalarticles and cured in mid-day summer sunlight in Virginia for one hour.The resulting coatings had a contact angle to water of 120°. The surfacearea population of trifluoromethyl groups exceeded 70%.

EXAMPLE 11

A highly hydrophobic coating for spraying or dipping was prepared. Thecoating was provided from a coating formulation having a perfluorinatedhardenable resin. The coating formulation had the following ingredients:

10 parts by weight Teflon AF 1600 from DuPont

100 parts by weight FC-40 from 3M

1 part by weight L-9187 polymer from Cytonix Corporation

The ingredients were mixed and heated to 120° C. for two hours. Theresultant material was then painted onto glass, PTFE and metal articlesand cured in an oven at 200° C. for one hour. The resulting coatings hada contact angle to water of 120°. The surface area population oftrifluoromethyl groups exceeded 90%. The surface energy of the coatingwas below 9 dynes/cm compared to the surface energy of articles coatedwith Teflon AF alone, which was about 16 dynes/cm. The properties of theinventive coating indicate a substantially perfluorooctyl surface on thecoatings of the present invention.

Although the present invention has been described in connection withpreferred embodiments, it will be appreciated by those skilled in theart that additions, modifications, substitutions and deletions notspecifically described may be made without departing from the spirit andscope of the invention defined in the appended claims.

What is claimed is:
 1. A process for coating an article with ahydrophobic material comprising a polymerization product of afluorinated monomer, said process comprising the steps of:providing anarticle having a surface to be coated which is intended to be exposed toweather; applying a first coating composition to at least a portion ofthe surface and forming a coating on said surface from said composition,said coating comprising a reaction product of a fluorinated reactanthaving from about 3 to about 20 carbon atoms and at least one terminaltrifluoromethyl group, said coating composition further comprising asecond component, said second component comprising a hardenablematerial, said composition forming a coating having an exposed coatingsurface area populated with at least about 15% by area trifluoromethylgroups and a surface energy of about 22 dynes/cm or lower at 20° C.,hardening said coating to form a hard hydrophobic coating.
 2. Theprocess of claim 1, wherein said hardenable material comprises at leastone resin selected from the group consisting of acrylics, cellulosics,epoxies, polyesters, silicones, urethanes, and combinations thereof. 3.The process of claim 1, wherein said article is a vehicular surface, anarchitectural surface, a windshield, a rainshield, outdoor furniture, asignal receiving or emitting device, an antenna, a radar dish, amicrowave antenna, a radome, a reflector, a sign, or a display device.4. The process of claim 1, wherein said article comprises a radome or acomponent of a radome.
 5. The process of claim 1, wherein said reactionproduct comprises a polyperfluoroalkyl polymer.
 6. The process of claim1, wherein said second component comprises a non-fluorinated hardenableresin.
 7. The process of claim 1, wherein said second componentcomprises a fluorinated hardenable resin.
 8. The process of claim 1,wherein said coating composition further comprises a surface rougheningagent which provides a rough surface to said coating.
 9. The process ofclaim 1, wherein a surface roughening agent is adhered to said coatingcomposition after said composition is applied to said surface.
 10. Theprocess of claim 1, wherein said coating composition further comprises afluorinated solvent.
 11. A process for forming a hydrophobic coating onsurfaces of articles, said process comprising:containing articles in theinterior of a sealed container along with a coating composition, saidcoating composition comprising a reaction product of a fluorinatedreactant, said coating composition further comprising a substantiallyfluorinated solvent; causing said articles to contact said coatingcomposition in said interior at a vapor pressure below 25% ofatmospheric pressure to form coatings on said articles; separating thecoated articles from remaining coating composition; and breaking theseal of the container while the vapor pressure in the interior is below25% of atmospheric pressure.
 12. A process as in claim 11, wherein saidvapor pressure is below 10% of atmospheric pressure.
 13. A process as inclaim 11, wherein when said articles contact said composition thetemperature of the solvent is maintained below 75% of the absolute valueof the difference between the boiling point of said solvent and 25° C.